One of the important goals of research on Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is the identification of mycobacterial antigens that induce protective T-cell responses and/or stimulate humoral immunity during tubercular infection. Antigens in the former class constitute potential candidates for the development of effective vaccines, while those in the latter group can be tested as new, improved tools for diagnosis of TB.
Similarly, numerous other bacterial pathogens have pathogenicity that, as with TB, is not caused by a single protein, as is the case also with parasites generally. Antigens produced by these pathogens are also potential candidates for the development of effective vaccines.
Proteins that are actively secreted by M. tuberculosis have attracted considerable attention as potent immunogens. The observation that only live, dividing mycobacteria efficiently induce protective immunity (7, 22) led to the hypothesis that proteins that are actively secreted by M. tuberculosis during growth are key in generating protective T-cell responses (4, 23). Indeed, experimental vaccines based on culture filtrate proteins have been shown to induce some levels of protective immunity in animal models of TB (5, 14, 15, 26). Secreted proteins of M. tuberculosis are also potent inducers of antibody production (13).
The identification and immunochemical characterization of individual components of M. tuberculosis culture filtrates is a crucial step toward understanding the role of the secreted proteins in inducing immune responses during the course of TB. More than 30 proteins are present in filtrates from short-term (4-5 day) cultures (3), prior to any substantial contamination of the filtrates by intracellular components released by autolysis of aging cells. Only about ten actively secreted proteins have been identified using antibodies from immunized animals (1); most of them have been characterized by gene cloning and nucleotide sequencing (2, 6, 9, 11, 17-20, 29, 34). Some of the known secreted proteins induce cellular immune responses (35); however, strong human T-cell responses to secreted protein fractions involve yet uncharacterized antigens in the cell filtrate (8, 29).
An aspect of this invention is an isolated DNA sequence encoding the amino acid sequence of the MPT63 antigen, a protein secreted by M. tuberculosis, that is specific for mycobacterial species that belong to the M. tuberculosis complex, as well as recombinant polypeptide sequences encoded by that DNA.
Another aspect of this invention is an isolated DNA sequence encoding the amino acid sequence of the MTC28 antigen, another protein secreted by M. tuberculosis that is similarly specific, as well as purified natural and/or recombinant polypeptide sequences encoded by that DNA.
Another aspect of this invention is a "cocktail" of purified natural and recombinant protein antigens or polypeptides for immunodiagnostics or vaccines, as well as DNA cocktails for vaccines.
Other aspects of this invention are in vitro and in vivo methods of detection of immune responses using the protein or polypeptide cocktails and DNA cocktails of this invention.